Principle of this test

Performic acid oxidation is performed prior to hydrolysis to oxidize cystine and methionine to cysteic acid and methionine sulfone, respectively. Sodium metabisulfite is added to decompose performic acid. Amino acids are liberated from protein by hydrolysis with 6M HCl. Hydrolysates are diluted with sodium citrate buffer or neutralized, pH is adjusted to 2.20, and individual amino acid components are separated on ion-exchange chromatograph. Tyrosine is destroyed by oxidation. Tryptophan is destroyed by hydrolysis, so those amino acids cannot be determined.